.item {
    position: relative; /* or absolute */
}

.item:before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: transparent;

    box-shadow: -50px 80px 4px 10px #555;
    -webkit-transform: rotate(10deg);
    -moz-transform: rotate(10deg);
    -o-transform: rotate(10deg);
    -ms-transform: rotate(10deg);
    transform: rotate(10deg);
}